U.S. patent number 3,704,893 [Application Number 05/069,737] was granted by the patent office on 1972-12-05 for piston ring.
This patent grant is currently assigned to Eaton Corportion. Invention is credited to Donald C. Hill.
United States Patent |
3,704,893 |
Hill |
December 5, 1972 |
PISTON RING
Abstract
An internal combustion engine piston having a live head-land
ring whose cross-section is imbalanced by differentiating it from a
circumscribing circle whose diameter equals the maximum diagonal
dimension to exterior corner points (which, in the case of a ring
having a blunted corner or tapered face, will be the virtual corner
point) of the ring when free and unconfined, so that more material
is omitted within the inner-upper and outer-lower quadrants than
within the inner-lower and outer-upper quadrants, or vice versa,
depending upon the sense in which torsional twist is desired when
the ring is contracted to cylinder diameter.
Inventors: |
Hill; Donald C. (Concord
Township, St. Louis County, MO) |
Assignee: |
Eaton Corportion (Cleveland,
OH)
|
Family
ID: |
22090904 |
Appl.
No.: |
05/069,737 |
Filed: |
September 4, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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865593 |
Oct 13, 1969 |
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Current U.S.
Class: |
277/451; 277/453;
277/466 |
Current CPC
Class: |
F16J
9/00 (20130101) |
Current International
Class: |
F16J
9/00 (20060101); F16j 009/20 () |
Field of
Search: |
;29/156.6
;92/181,182,193,194,246
;277/1,168,173,174,178,216,225,58,78,170,171 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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587,913 |
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May 1947 |
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GB |
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356,943 |
|
Sep 1931 |
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GB |
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29,563 |
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Nov 1905 |
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GB |
|
Other References
Braendel, H. G., Late Trends in Piston Rings with Special
Application to Diesel Engines, in Diesel Power and Diesel
Transportation, pg. 37-41, 6/19/47..
|
Primary Examiner: Earls; Edward J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of my prior copending
application Ser. No. 865,593, filed Oct. 13, 1969 now abandoned.
Claims
Having thus described the invention, what is claimed and desired to
be secured by Letters Patent is:
1. The combination with an internal combustion engine cylinder and
piston having a head surface which, with the walls of said
cylinder, circumscribe a combustion chamber, of a one piece live
head-land piston ring having a free gap of approximately between 7
percent and 16 percent of the installed diameter, said ring having
a cross-section of a type which may be controllably unbalanced,
said cross-section being unbalanced in the direction such that as
the gap in the ring is contracted the ring twists, and means for
mounting said ring on said piston with its uppermost side surface
entirely exposed to gases in said combustion chamber.
2. The combination of claim 1 wherein said means comprises a rib
integral with, and extending circumferentially of, said piston at a
substantial distance below said head surface, and a
circumferentially extending channel on the inner periphery of said
ring, said channel and said rib being shaped to interfit with
freedom for relative circumferential and radial movement and with
restraint against substantial relative movement in the axial
direction.
3. The combination of claim 2 wherein said rib and said channel
have cross-sectional shape of a truncated triangle.
4. The combination of claim 2 wherein said rib has a substantially
greater outer circumference than does said head surface.
5. The combination of claim 4 wherein said ring has a flange
overlying said rib and extending upward therefrom toward alignment
with said head surface.
6. The combination of claim 1 wherein said upper side face of said
ring is substantially aligned with said piston head surface.
7. The combination of claim 1 wherein said ring has oppositely
oriented halved laps at said gap and movably bridging the same to
obstruct the flow of gas from said cylinder past said ring.
8. The combination with a cylinder and a piston having a head
surface which, with the walls of said cylinder, circumscribe a
chamber, of a one-piece live head-land piston ring having a free
gap of approximately between 7 percent and 16 percent of the
installed diameter, said gap being substantially closed when said
piston ring is installed in said cylinder to sealingly engage a
peripheral surface of said cylinder, said piston ring having a
cross-section of a type which may be controllably unbalanced, said
cross-section being unbalanced in the direction such that as the
gap in the ring is contracted the ring twists, and means for
mounting said ring on said piston with its uppermost side surface
entirely exposed to gases in said chamber.
9. The invention of claim 8 wherein the cross-section of said
piston ring is T-shaped with the tongue of said T extending
inwardly from the periphery of said ring and wherein approximately
4 percent more of the cross-bar of said T lies on one side of said
tongue than lies on the other side of said tongue whereby a
controlled amount of torsional twist exists in the cross-section of
said ring when said ring is confined to said predetermined
diameter.
10. The combination of claim 9 in which more of said bar lies above
a radial plane bisecting said tongue than lies below said bisector
whereby the ring has positive twist when contracted from its free
and unconfined condition.
11. The piston ring of claim 9 wherein the portion of said bar
lying on one side of said tongue is approximately 31 percent of the
length of said bar and the portion lying on the other side of said
tongue is approximately 27 percent of the length of said bar.
12. The combination of claim 8 wherein the cross-section of said
ring is T-shaped.
13. The combination of claim 8 wherein the cross-section of said
ring is U-shaped.
14. The combination of claim 13 wherein one leg of the U-shape is
shorter than the other to produce a J-shape.
15. The invention of claim 8 wherein the cross-section of said
piston ring is a substantially U-shaped configuration with the legs
of said configuration extending radially inwardly from the
periphery of said ring and wherein one of the legs of said
configuration contains slightly more piston ring material than the
other leg whereby a torsional stress exists in the cross-section of
said ring when said ring is confined to said predetermined
diameter.
16. The invention of claim 15 wherein the internal surfaces of the
legs of said substantially U-shaped cross-section are tapered
outwardly.
17. The invention of claim 15 wherein said piston ring is made of
Piston Ring Gray Iron.
Description
This invention relates generally to reducing the emission of
atmospheric pollutants from internal combustion engines, and
particularly to the relationship between a piston ring and a piston
having a head-land groove.
Some internal combustion engines have heretofore had a relationship
between piston and piston ring wherein the piston ring (sometimes
called the "fire ring") closed to the combustion chamber is
accommodated in a ring-groove whose upper land is either absent or
of substantial lesser outside diameter than other lands, whereby a
substantially greater increment of the upper side of the fire ring
is exposed to the cylinder gases than would be exposed in the more
common arrangement where the clearance between any land and the
adjacent cylinder wall seldom exceeds 0.050 inch at each end of a
diameter. In some cases, such land between the fire ring and the
combustion chamber is an integral part of the piston, and in other
cases it is separable, but, in either event, the arrangement has
come to be known in the art as the "head-land ring" construction,
and has gone into considerable use in two-stroke cycle gasoline
engines where the rings are "dead." The line of demarcation between
"dead" and "live" rings is not precisely defined by an industrial
standard, and there is latitude in each; but for the purpose of
this disclosure, a ring may be considered "dead" when its internal
stress at installed diameter is less than 40 percent of the maximum
internal stress that could exist without exceeding the rupture
strength of the material either as a finished ring or during the
machining process. In explanation, reference may be had to FIG. 4
of U.S. Pat. No. 1,779,487 wherein the three uppermost rings are of
square cross section. If made of conventional "Piston Ring Gray
Iron" (SAE J929) with casting size as required to machine to a
width and thickness of one-eighth inch (.+-. standard tolerances),
the material in said casting for such a ring (hereinafter called
the "archetypal ring") will have a rupture strength of
approximately 60,000 PSI. The casting (in complete circular form,
i.e., without any gap) is machined and a portion removed to provide
a gap (known in the art as "free gap"), which is the gap that
exists when the ring is free of all external confining forces.
Given the archetypal ring of peripheral length appropriate for use
in a cylinder having a nominal 2.82 inch diameter, the free gap
cannot exceed 0.462 inch without peril of overstressing the ring
metal under diametrical tension to close, which in the case of the
archetypal ring could not exceed approximately 11.25 pounds.
"Diametrical tension to close," as the expression is used herein,
means the magnitude of force applied at diametrically opposite
points, in approximate quadrature with the gap of a ring, to so
partially close the gap therein that the distance between said
diametrically opposed points equals the "installed diameter," which
is the diameter of the cylinder in which the ring is to be
installed. All other variables remaining constant the diametrical
tension to close decreases as the length of the free gap decreases,
but when the free gap equals the installed gap, the diametrical
tension to close loses all significance because the tension of the
ring as installed is zero, which is the ultimate of "dead."
In one contemporary version of the head-land ring construction, the
ring is L-shaped (or "angle bar" section), and in another version
the ring is of "half-keystone" section typified in FIG. 6 of U.S.
Pat. No. 2,459,395. If either of these versions is "live" by virtue
of having anywhere near a normal amount of free gap, it will, when
the gap is closed, or nearly closed, within the cylinder, assume an
excessive "torsional twist."
"Torsional twist" is considered excessive when it averages
substantially more than about 0.001 inch twist per 0.100 inch of
radial thickness of a ring, which may be angularly expressed as
about 54 minutes. Rings with excessive torsional twist tend toward
breakage resulting from flexing as the cylinder gas pressures tend
to untwist them. In the parlance of the art, such twist is
"positive" when it tends to force the outer-lower corner of a ring
toward a greater diameter than the outer-upper corner; and is
negative when it tends to force the outer-upper corner of a ring
toward the greater diameter. As used herein, the term "upper"
connotes that the subject is closer to the combustion chamber than
is its counterpart, designated "lower." Likewise, "outer" connotes
that the subject is closer to the cylinder wall than is its
counterpart, designated "inner."
When such rings are deadened to avoid the undesirable effects of
excessive twist, as has been done by some manufacturers in some
applications of head-land rings, there is a tendency toward
breakage which results from the lack of tension. In order to reduce
the breakage in such a "dead" ring, such manufacturers have been
forced to use more expensive, high strength special iron in the
manufacture of such rings. However, a ring which is substantially
without intrinsic tension, or "dead," is free to flutter under the
influence of the changing pressures during the continually
reversing strokes of an internal combustion engine. It is this
fluttering which exceeds the dampening capacity of the gray iron
(from which piston rings are normally cast) and causes breakage. If
such rings had substantial intrinsic tension, the need for the high
strength special iron, or other such extraordinary materials of
construction, would be eliminated, or at least reduced.
Accordingly, it is one object of the present invention to provide a
head-land piston ring in which internal stresses are coordinated to
stabilize the ring during operation, and thus to reduce the need
for making them of special high strength metal.
Although improved performance has been claimed for the dead ring
concept when used as a head-land ring, this design requires the
building up of gas pressure in the combustion chamber of the
engine, and behind the ring, to seat the ring against both the
lower side of its groove and the cylinder wall, with consequent
leakage occurring between the ring and the cylinder wall during the
time that the pressure is building up. Such leakage would not have
occurred, at least in anything like the degree in which it does
occur, if the ring inherently biased itself against the cylinder
wall by virtue of its intrinsic tension. In some four-stroke cycle
engines, the dead L-shaped head-land ring has required a coil
spring in compression behind it to provide extrinsic tension which
results in the face of the ring being held in contact with the
cylinder wall during the suction stroke. Such expedients are
unsatisfactory because of their proclivity to carbon up, and
thereby lose effectiveness. It is therefore another object of the
invention to eliminate the need, with head-land rings, of such
auxiliary devices.
A further object is to improve performance of, and reduce the
emission of atmospheric pollutants from, internal combustion
engines having a head-land ring.
These and other objects and advantages of the invention are
achieved, in accordance with the present invention, by making
head-land rings of ordinary piston ring material, (i.e., ordinary
"Piston Ring Gray Iron," in contrast with the special high strength
iron alloy) but with controllably imbalanced cross-sectional
configurations, mounting means, and gap-bridging, all coordinatable
to produce optimum results under a wide diversity of operating
conditions. The ring per se may have any of a variety of
cross-sectional shapes such as on-side T-shape, on-side J-shape, or
on-side U-shape, so long as they are cross-sectionally unbalanced
in a manner such as to produce the desired twist when the ring is
contracted from its free and unconfined state to the diameter of
the cylinder in which it is installed, such contraction being
achieved by moving the opposed gap-ends toward each other, thereby
reducing the circumferential length of the gap, and the normal
perimeter of the ring (including gap). Such contraction
substantially increases the "tension" of any ring which is "live,"
and, if the ring has an unbalanced cross-section, induces twist in
it.
Such a "live" ring of unbalanced cross-section may be mounted on
the piston so as to have its upper side face in substantial
alignment with, or deliberately disaligned from, the head face of
the piston, and it may have said upper side face partially covered
by a land, or completely exposed to the hot gases in the combustion
chamber. However, any land, even partially covering the upper side
face of a ring in immediate adjacence to the head face of the
piston has been found to run substantially hotter than the piston
head face area radially inward thereof, and manifests itself by
excessive carbonization on such a land. Accordingly, it is
preferred that the head-land ring be so mounted on the piston that
its upper face of the ring is substantially, if not completely,
exposed to the hot gases in the combustion chamber.
If it becomes desirable to reduce the intrinsic tension of such a
ring, the magnitude of its free gap may be reduced and its
cross-sectional imbalance changed appropriately to achieve the
desired twist at the reduced tension. The latter is accomplished by
changing the proportionate amount of material omitted from the
inner-upper and outer-lower, vis-a-vis that omitted from the
inner-lower and outer-upper quadrants of a virtual circular section
whose center is at the midpoint of the diagonal between the desired
ring's most remote corner points (or virtual corner points, in the
case of a ring having blunted corners or a conical or spherical
peripheral face) while in its free and unconfined state, so as to
adjust twist back to where it was before the magnitude of the free
gap was changed or to any chosen degree or sense. Thus, it is
possible to make the ring with either positive or negative twist,
or with no twist at all; and the same ring with a cylindrical or
convex face at its outer periphery can have the sense of its twist
reversed by merely turning it over. There is no need to back up
such a ring with an auxiliary spring device that sooner or later
would carbon up and become ineffective, and the designer has
complete latitude in his selection of the specifications to which
the part will be machined, at least to the same degree that he has
had in designing the more conventional torsional or non-torsional
rings heretofore in use.
The ability to vary tension and twist in rings, so as to suit the
needs of individual engines, has always been desirable, but it is
not possible to make such adjustments in design in a head-land ring
which is "dead." Furthermore, the rings contemplated by the present
invention are usable in grooves more remote than a head-land groove
from the head of the piston as a replacement for, or in addition to
its use as, a head-land ring.
Several embodiments of head-land rings - which when made of Piston
Ring Gray Iron, and otherwise in accordance with the invention
will, with normal (e.g., about 70to 16 percent of the installed
diameter) free gap, not only twist when contracted to installed
diameter, but will exhibit a diametrical tension to close
equivalent to approximately 50 to 90 percent of the rupture
strength of the iron--are illustrated in the accompanying drawings,
in which:
FIG. 1 is a perspective view of a typical piston for a two-stroke
cycle engine equipped with a head-land ring constructed in
accordance with the present invention;
FIG. 2 is a partial sectional view taken along plane 2--2 of FIG.
1, and showing one possible relationship of the ring to a cylinder
wall;
FIG. 3 is a perspective view of a typical piston for use in a
four-stroke cycle engine, and having a ring belt including a
head-land ring constructed in accordance with the present
invention, a conventional intermediate ring, and a conventional oil
ring;
FIG. 4 is a partial sectional view taken along plane 4--4 of FIG.
3, and showing one possible relationship of the rings with a
cylinder wall;
FIG. 5 is a perspective view, showing the gap end, of a head-land
ring embodying the invention, and having a cylindrical outside
face;
FIG. 6 is a view corresponding to FIG. 5, but showing an embodiment
of the head-land ring having a "taper face", i.e., one in which the
outer face is generally conical;
FIG. 7 is a view corresponding to FIG. 5, but showing a head-land
ring having a convex or "barrel" shaped outside face in which the
face is arcuate in radial section;
FIG. 8 is a diagrammatic view showing (in somewhat exaggerated
degree) the relationship of the ring in FIG. 5 with the piston and
the cylinder when the ring has positive twist and is contracted to
cylinder diameter;
FIG. 9 is a view corresponding to FIG. 8, but showing the ring of
FIG. 8 turned upside-down to produce negative or reverse twist;
FIG. 10 is a perspective view of a complete ring constructed in
accordance with the embodiment shown in FIGS. 1-5, 8 and 9;
FIG. 11 is a perspective view comparable to FIG. 10, but showing a
head-land ring of on-side U-shaped cross-section with a gap defined
by a halved lap joint;
FIG. 12 is a sectional view taken along line 12--12 of FIG. 11,
showing the ring of FIG. 11 as mounted upon a piston and within a
cylinder;
FIG. 13 is a sectional view comparable to FIG. 12, but showing a
ring having a modified form of on-side U-shaped cross-section with
an appropriate mounting land;
FIG. 14 is a cross-sectional view comparable to FIGS. 12 and 13,
but showing a ring of on-side J cross-section mounted upon a piston
within a cylinder;
FIG. 15 is a perspective view of the ring shown in FIG. 14; and
FIG. 16 is a diagrammatic view illustrating a graphical method of
predetermining the sense and degree of torsional twist induced by
closing the gap of a ring of the general type illustrated in FIGS.
14 and 15.
In the form shown in FIGS. 1 and 2, the piston has a head 1, a
skirt 2, and a single head-land groove 3 to accommodate a T-shaped
ring of the form illustrated in FIG. 10, whose tongue 4 interfits,
with clearance, within groove 3, and whose bar 5 has its outer face
6 in contact with the cylinder wall 7, while its upper side 8 is
exposed to the cylinder gases. From FIG. 5, it will be apparent
that the bar 5 of the ring is unbalanced with respect to tongue 4,
that is to say, that the horizontal center line of tongue 4 is not
coincident with the horizontal center line of bar 5. Such
eccentricity, in the embodiment illustrated, amounts to 31 percent
of the width (i.e., the vertical dimension as seen in FIG. 5) of
the ring, lying above the upper surface 4' of tongue 4. On the
other hand, but 27 percent of the width of the ring lies below the
lower surface of tongue 4. These proportions of imbalance between
the bar and the tongue of the ring produce twist of about 36
minutes, having a sense indicated by the curved arrow on FIG. 5 to
produce the ring-groove-cylinder relationship, shown in FIG. 8,
when the ring is contracted to cylinder diameter with corner 9
urged, by virtue of the twist, into engagement with the cylinder
wall. If the ring shown in FIG. 5 be turned upside down, and
contracted from its free and unconfined state to an outside
circumference which is approximately that of the cylinder in which
it is to operate, the twist will be as shown in FIG. 9 and be
termed "negative" or "reverse," but nevertheless continuing to tend
to move corner 9 into a position of greater circumference than
corner 10, because corner 9 will now (FIG. 9) be at the upper side
rather than at the lower side as shown in FIGS. 5 and 8.
As is well known, increasing the imbalance in the relationship of
the bar 5 to the tongue 4 increases the degree of torsional twist,
all other things (notably free gap) remaining constant. In
operation, where such a live ring with normal gap and normal twist,
is used in a cylinder whose internal circumference is less than the
free and unconfined outside circumference of the ring, the effect
of the cylinder gas pressure upon the ring is illustrated in FIG.
8, where it will be observed that the pressurized cylinder gases
have free access to the space 11 between the inner face 12 of the
ring and the outer face of head-land 13 on the piston. The local
effect of the pressurized gases within space 11 is therefore to
urge the ring, or at least the upper increments thereof, in a
radially outward direction from land 13, and toward cylinder wall
7. At the same time, however, the pressurized cylinder gases have
access to the space 14 between the surface 4' of the ring and the
side 15 of the ring groove 3. Such pressure within the space 14
acts on a larger area than at face 12, and hence exerts a greater
force axially with the local effect of driving the tongue of the
ring downwardly toward the opposite side 16 of the groove 3.
Furthermore, the same pressurized gases occupy the space between
the back 17 of the ring and the bottom 18 of the groove, and have
the local effect of tending to drive the ring radially outward
toward engagement with the cylinder wall 7. The inherent twist in
the ring, by virtue of it having been contracted from its free gap
condition, operates counter to some of these local effects, and
tends to move corner 19 of the ring into sealing engagement against
groove side 16 at the same time that corner 9 of the ring is urged
into sealing engagement with the cylinder wall 7.
The effects with the same ring turned upside down to create a
negative twist are illustrated in FIG. 9, where the effect of twist
is to urge point 20 on surface 4' (now addressed downwardly) into
engagement with groove side wall 16, and to drive corner 9 (now at
the upper side) into engagement with cylinder wall 7. However, such
turning upside-down does militate against one desideratum, to wit,
that (at least during the compression and power strokes) the
lowermost side surface of the bar 5 be in substantially sealing
contact with the shoulder of the groove adjacent corner 9 as seen
in FIG. 8, or adjacent corner 10 as seen in FIG. 9; and that the
corner 19 of the tongue 4 have approximately zero clearance with
groove side 16 (in the case of FIG. 8) or the groove side 15 (in
the case of FIG. 9). While, for clarity of illustration in FIGS. 8
and 9, the relationship of ring and groove is shown with space
between the lowermost side surface of the bar 5 and the adjacent
shoulder of the groove, those skilled in the art will understand
that sealing contact is intended to be made there at least during
the compression and power strokes.
The configuration of the outer face 6, shown cylindrical in FIGS.
1-5, 8, 9 and 10, is subject to conventional variation in contour
for specific known effects without adversely affecting the
advantageous performance of the ring. For example, the face 6 may
have conical aspect as shown at 66 in FIG. 6, which is sometimes
known in the art as a "taper face." Alternatively, the face 6 may
be contoured to the form known in the art as a convex or barrel
face 60, as shown in FIG. 7, wherein the cylinder-engaging face of
the ring is an arc of a circle whose center lies on the diameter
which bisects the face 60. A further alternative is to make the
convexity of face 60 eccentric by having the center of its
curvature on a diameter of the ring which does not bisect the face
60, thereby either adding to or subtracting from the twist induced
by the imbalance of the bar relative to the tongue of the T-shaped
section. Likewise, the amount of twist can be coordinated with the
degree of taper on face 66 of FIG. 6 to produce variations in the
"tension" exerted at 69 and clearance at 68. To assure such
clearance with a ring which has positive twist, or no twist at all,
the amount of taper in face 66 is normally about 1.degree. off
parallel with the axis of the ring when free and unconfined. As
previously explained, such clearance would be at the lower side
when the ring is turned upside down from the orientation shown in
FIG. 6. While such relationship between the face 6 and the cylinder
wall 7, as illustrated in FIG. 9, is quite satisfactory for
operation in a two-stroke cycle engine, it is less desirable in a
four-stroke cycle engine where the direction of taper would, for
this application, be reversed and the degree thereof increased to
assure that the lower corner 10 contacts cylinder wall 7, and that
clearance exists between the top corner 9 (as seen in FIG. 9) and
the cylinder wall 7.
Similarly, the relationship between the barrel face 60, of the ring
shown in FIG. 7, with the cylinder wall assures initial clearance
at both the upper and lower outer corners of the ring regardless of
whether the ring is upside up or upside down, and when the ring 60
is utilized in the reverse twist orientation the face convexity may
be greater (i.e., the radius may be shorter) than that which
obtains when the barrel-faced ring has positive twist.
Not only does the head-land ring of the invention lend itself to
use in two-stroke cycle engines, but it can also be used, with
advantage, in four-stroke cycle engines. A four-stroke cycle
installation is illustrated in FIGS. 3 and 4, where a typical
piston has a head 31, a skirt 32, a head-land ring groove 33, an
intermediate ring groove 43, and an oil ring groove 53, but the
head-land ring can be of identical configuration with any of the
embodiments hereinbefore described so as to provide a T-shaped
cross-section with the tongue 34 thereof extending substantially
perpendicular with the direction of piston reciprocation, while the
bar 35 thereof extends substantially parallel (albeit twisted) with
the direction of piston reciprocation. Moreover, the relationship
of the T-shaped head-land ring, relative to the cylinder wall 36
and the groove 33, is subject to all of the variations in contour
and orientation, with the same effects as those hereinbefore
described in connection with the ring for the two-stroke cycle
engine.
While in the embodiments shown in FIGS. 1 through 10, the omission
of material to create the cross-sectional imbalance which induces
twist is confined to the exterior of the ring, other embodiments
now to be described involve the converse treatment, to wit: that
the omission of material to create the desired imbalance occurs, at
least in part, on the interior of the ring. Likewise, whereas in
the embodiments previously described, only the upper side face of
bar 5 is exposed at all times to the cylinder gases, the
embodiments now to be described are so cross-sectionally
configurated and mounted that the entire upper surface of each is
completely exposed to the cylinder gases, and can be substantially
flush with the head face of the piston.
In the embodiment of the invention illustrated in FIGS. 11 and 12,
it will be observed that the piston 71 has a foreshortened land 72
near, but in substantially spaced relationship from, the head face
73 of piston 71 and another land 72a of larger diameter spaced
further from the head 73 of the piston 71 than the foreshortened
land 72. The head-land ring 74 is provided with rabbet 75 at its
inner periphery. The rabbet 75 is proportioned to accommodate land
72 with freedom for movement relative thereto. Also, the rabbet 75
is eccentric in both the axial and radial dimensions of the ring,
thus creating a lesser axial dimension in the upper leg 76 of the
ring than in the lower leg 77 thereof. Such imbalance of the
cross-section of the ring 74 induces the desired torsional twist
when the ring is contracted from its free and unconfined condition,
as shown in FIG. 11, to an outside diameter substantially equal to
the inside diameter of cylinder wall 70.
The ring shown in FIGS. 11 and 12 is further characterized by the
feature that its gap ends 78 and 79 are formed after the fashion of
a halved lap joint, so that when the ring is contracted from its
free and unconfined condition shown to the diameter of a cylinder
in which it is installed, the respective halved laps will be in
overlapping relationship. Hence, even with a substantial installed
gap, there will be no such direct or unimpeded vent between the
ring ends as is the case when the ring ends are chamfered or
butt-like, as shown in FIG. 10.
FIG. 13 shows a modification of the arrangement shown in FIG. 12,
the only differences being that the eccentric rabbet 85, instead of
having the rectangular configuration shown in FIG. 12, has a
keystone shape; and that the exterior surfaces of stub land 82 are
configurated to mate (with appropriate clearance) with the internal
configuration of rabbet 85. This construction reduces the tendency
of the ring to stick in the course of normal expansion and
contraction and is of special utility in worn cylinders, as proved
by a comparative test in a Pontiac engine whose cylinders were worn
to a taper of 0.008 to 0.010 inch, and were out of round. The
pistons were first equipped with a conventional replacement ring
set (i.e., without a head-land ring) and the engine operated under
standard test conditions to measure oil consumption and the
blow-by. Then the upper land of each piston was reworked to provide
a stub land of the form, and at the position, of 82, i.e., so that
the upper side face 88 of each ring would be completely exposed to
the cylinder gases, as shown in FIG. 13. The other grooves were
equipped with duplicates of the rings employed in the first test,
and are typified by rings 43 and 53 in FIG. 4. The so equipped
pistons were installed in the same engine and operated as in the
first test, with the result that oil consumption was substantially
unchanged, but blow-by was reduced to 60 percent of that measured
in the first test. Thus, the comparative tests demonstrated a
substantial reduction in the emission of atmospheric
pollutants.
The combination of the keystone-shaped concavity 85 in the ring 88
with the keystone-shaped convexity of the land 82 may, with
efficacy, be applied in reverse order to the on-side T-shaped rings
shown in FIGS. 2 and 5 through 9 by making the tongue 4 of convex
keystone shape and making the groove 3 of companion concave
keystone shape. In such application, the desired torsional twist,
if any, can be achieved either by adjusting the eccentricity of the
keystone tongue relative to the bar 5, or by machining the opposite
faces of the keystone tongue at different slopes.
A further modification is shown in FIG. 14, wherein an on-side
U-shaped ring is imbalanced by having its upper leg 96 bobbed and
made to have the same axial dimension as lower leg 97, thereby to
produce a species of U-shaped sometimes called a J-shape. Since leg
96 is of lesser radial dimension than leg 97, there is produced an
unbalanced cross-section to achieve the desired twist. Between the
upper and lower legs 96 and 97, there is a rabbet 95 of uniform
axial dimension. As in the previous embodiments, stub land 92 is
accommodated in the rabbet 95, but in the case of the ring shown in
FIG. 14, the corner 90 of the piston head 91 extends closer to the
cylinder wall than in FIGS. 12 and 13, and is so arranged that the
upper side face of ring 94 is substantially flush with the head
face of piston 91 without being overhung by a land.
As illustrated in FIG. 15, the ring shown in FIG. 14 is equipped,
as in the previous embodiments, with a gap defined by a halved lap
joint.
In the embodiments of FIGS. 12, 13 and 14, the outer peripheral
faces of the rings can be given any of the conventional shapes
typified in FIGS. 5, 6 and 7, and can have the sense of their twist
reversed by turning them upside down, albeit requiring appropriate
modification of the stub land and groove on the piston. However, it
will be observed that in FIGS. 12, 13 and 14, there is no land on
the piston which overhangs the upper surface of the head-land ring.
Consequently, the upper surface of the head-land ring is completely
exposed to the hot gases in the combustion chamber. This
arrangement has been found to have a decided advantage over the
arrangements shown in FIGS. 1 through 6, wherein a stub land does
overhang at least part of the upper side face of the ring. Such an
overhanging stub land does not freely dissipate its heat, but tends
to store it, and hence becomes hotter than any other part of the
piston, as evidenced by the observation that with constructions
wherein a stub land overhangs part of the upper face of a head-land
ring, a band of severe carbonization occurs, and the greater the
degree of the carbonization, the more heat dissipation is retarded,
with resultant loss of efficiency and increase in pollutant-laden
exhaust.
Thus it will be apparent to those skilled in the art that the rings
of the invention lend themselves to any of the conventional ring
face treatments, such as tin plating, chromium plating, or the
application of ceramic and other non-metallic surface treatments.
Their corners can be square or blunted as by beveling or rounding,
and their outer faces can be cylindrical or tapered or otherwise
contoured, and can be grooved and filled with sprayed metal, or
other fillers applied by spraying, plating, inlay, or other
conventional means. Moreover, the back of the rings (identified as
surface 17 in FIG. 8) in all embodiments can be operated upon in
any conventional way to vary the degree of torsional twist, or to
expose more or less side area or back area to the pressure of the
cylinder gases than would be provided by the square rectangular
relationship shown in the several figures.
In order to elucidate a graphical method of predetermining the
sense and degree in which a head-land ring of the character herein
disclosed may be expected to exhibit torsional twist when
contracted to installed diameter from its free and unconfined
condition, reference may be had to FIG. 16, wherein a J-shaped ring
100, corresponding to that shown in FIG. 14, but having blunted
corners 101, 102, is circumscribed by a circle 103, which traverses
the actual inner-lower corner point 104, and traverses a virtual
corner point 105 adjacent blunted corner 102, and another virtual
corner point 106 adjacent blunted corner 101. The virtual corner
points 105 and 106 are positioned where the actual corners of the
ring would lie had they not been blunted. The circle 103 has a
diameter equal to the distance between actual corner point 104 and
virtual corner point 106, and the center of circle 103 is at the
mid-point of that diagonal.
To ascertain the sense and degree of torsional twist induced in any
ring, the circle 103 is divided into quadrants: OU designating the
outer-upper quadrant, OL designating the outer-lower quadrant, IU
designating the inner-upper quadrant, and IL designating the
inner-lower quadrant of the ring, as well as of the circle 103.
Those areas within the circle 103 which are not physically occupied
by the substance of the ring (shown cross-hatched) are delineated
by plus (+) or minus (-) signs, depending upon their orientation.
The so-delineated areas in quadrants IU and OL are delineated with
plus (+) marks to indicate that the subtraction of material from
the circular section to produce the cross-sectional shape of the
ring tends to produce torsional twist in the positive sense, i.e.,
in the counterclockwise direction, as seen in FIG. 16. On the other
hand, those areas delineated by minus (-) signs lie in quadrants OU
and IL, from which the subtraction of material from the circular
section to produce the ring cross-section (shown cross-hatched)
tends to produce torsional twist in the negative sense, i.e.,
clockwise. Accordingly, from the graphical analysis depicted in
FIG. 16, one skilled in the art can add the subtracted areas in
quadrant IU and quadrant OL to achieve a sum of the forces tending
to twist the ring in the positive sense when contracted from its
free and unconfined condition; and can add the subtracted areas in
quadrants OU and IL to achieve a sum of the forces tending to twist
the ring in the counterclockwise direction. Then by subtracting the
smaller of those sums from the larger of those sums, a mathematical
difference is achieved, the sign of which indicates the direction
of the twist, and the magnitude of which is indicative of the
degree of twist.
While several embodiments of the invention have been described in
detail, it is not to be understood that the invention is limited to
the specifics of those embodiments. On the contrary, it is to be
understood that the features of the invention are applicable
generally to head-land rings and the generation of intrinsic bias
and torsional twist therein by merely contracting the ring from its
free and unconfined condition to cylinder diameter, and for
controlling both the ring tension and the degree and sense of
torsional twist in an expeditious and convenient manner.
* * * * *